Docs: clarify usage of actions/setup-java with this action

[JoshMcCullough]

From the docs:

When using gradle-build-action we recommend that you not use actions/cache or actions/setup-java@v3 to explicitly cache the Gradle User Home. Doing so may interfere with the caching provided by this action.

I believe you are saying to just not enable the caching feature of actions/setup-java, but surely we can still use that action to install a specific JDK. Is that correct? If so, I can provide a PR to adjust the docs.

[bigdaz]

Yes, you can still use actions/setup-java: what's not recommended is using the cache: gradle option with setup-java like this.

I'll try to get the docs updated before the next release. A PR would be appreciated :).

[ankushg]

I believe this is also relevant: #561